The invention relates to an apparatus and related method applied in an Enhanced General Packet Radio Service (EGPRS) system, and more particularly, to a modulation scheme detecting apparatus and related method applied in an EGPRS system.
In EGPRS communication systems, each data block is encoded and modulated according to a designated modulation and coding scheme (i.e., MCS-1, MCS-2, MCS-3, MCS-4, MCS-5, MCS-6, MCS-7, MCS-8, or MCS-9). The EGPRS communication system adopts two kinds of modulation schemes. The first modulation scheme is Gaussian Minimum Shift Keying (GMSK), and the second scheme is 8-phase shift keying (i.e., 8-PSK or EPSK). In order to obtain higher throughput in a wireless environment, the selection of modulation schemes is dependent on the channel conditions and the requirement of services, such as data rate. In EGPRS communication systems, one encoded data block is modulated and transmitted over four successive bursts according to the same modulation scheme. The receiver of the EGPRS communication system has no idea about what scheme is utilized in advance. Therefore, to correctly read the received data, the receiver must detect the modulation scheme utilized by the transmitter.
One simple way to determine the modulation type is to use some kind of signaling between the transmitter and the receiver to indicate which modulation type is being used. However, this signaling decreases the information data rate and may therefore not be desirable. Another way to solve the problem without the need for additional signaling from the transmitting end is so-called blind modulation detection method, requiring both a GMSK demodulator and an 8-PSK demodulator in the receiver. The GMSK demodulator demodulates the received signal to generate a plurality of first data, and the 8-PSK demodulator demodulates the received signal to generate a plurality of second data. Then, one of first data and second data is selected according to the reception quality. For example, the one having the less number of error counts is selected. Since the GMSK and the 8-PSK demodulators are active simultaneously, significantly large memory space and computation effort are required. When available power consumption is taken into consideration for general mobile handsets, this conventional method apparently cannot meet user's need.
Therefore, there is a need for an efficient modulation detection technique that, in a simple and reliable way, detects the type of modulation used before the data demodulation is activated.